Manure nutrient management effects in the Leon River Watershed

Abstract

The Leon River Watershed (LRW) in central Texas is a Benchmark and Special Emphasis watershed within the Conservation Effects Assessment Project located in central Texas. Model simulations from 1977 through 2006 were used to evaluate six manure nutrient management scenarios that reflect realistic strategies that could be employed to reduce nutrient and sediment loadings in the LRW. Due to the presence of several dairies and a relatively large number of cows, special attention within this watershed is necessary to determine beneficial adjustments that can be made to protect water quality. The nutrient management scenarios analyzed reduced total nitrogen (N) and total phosphorus (P) loading in nearly all of the subbasins. Total N and total P loading was also reduced at the watershed scale; sediment load reduction was minor due to effective management measures already existing within the LRW. The percentage change in total N and total P loadings varied from an increase of 3% to a decrease of 11% and an increase of 5% to a decrease of 12%, respectively. The percentage change in sediment loadings varied from an increase of 22% to a decrease of 12% per subbasin. Model simulations conducted over a 30-year period for six manure management scenarios indicated that both total N and total P can be significantly reduced by employing additional nutrient strategies. This is the case whether the nutrients are removed from the immediate vicinity of the dairy or are transported outside of the watershed.